In applications, such as in a steam turbine, it is important to minimize the leakage between high and low pressure areas. One of the most problematic areas in minimizing leakage is between the rotating shaft and stationary structures such as diaphragms. Inherently, a gap or clearance exists between the rotating shaft and the stationary diaphragm where steam can leak through.
Ideally, these gaps or clearances are kept at a minimum, but the changing alignment of the rotating shaft with respect to the stationary diaphragm will limit how tight these gaps or clearances can be made. Additionally, fouling due to deposit build up from the motive fluid in the apparatus, can impede the operation of mechanisms designed to relieve interference caused by such changing alignment.
One technique to minimize the gap or clearance between the rotating shaft and the stationary diaphragm is the use of a floating labyrinth ring seal sized to fit within a cavity in the diaphragm, such as that disclosed in U.S. Pat. No. 5,403,019 to Marshall which is herein incorporated by reference. Although this seal provides a reasonably close gap or clearance, the seal would not work well when there is an abnormally small pressure difference across the seal. During a low pressure differential the stationary seal rests on the rotating shaft, prematurely wearing the stationary seal or the rotating shaft.